A self-levelling nano-g silicon seismometer 

Monday, 15 December 2014: 12:05 PM
William T Pike1, Aifric Delahunty2, Guangbin Dou2, Anisha Mukherjee2, Huafeng Liu2, Simon B Calcutt3 and Ian M Standley4, (1)Imperial College London, London, SW7, United Kingdom, (2)Imperial College London, London, United Kingdom, (3)University of Oxford, Oxford, United Kingdom, (4)Kinemetrics, Inc., Pasadena, CA, United States
We demonstrate a microseismometer with a 2ng/rtHz noise floor capable of autonomous operation over a wide range of tilts. This represents the highest performance yet achieved by a silicon-based vibration sensor. The microseismometer builds on previous development of a short- period seismometer for NASA’s 2016 InSight mission to Mars. The 25-mm-square sensor element is unique in that it uses a spring-mass system with a proof mass that moves laterally. This minimizes the damping of the spring mass systems without the need for vacuum encapsulation. The proof-mass position is sensed by a periodic linear capacitive array transducer allowing highly sensitive position detection combined with feedback control at multiple null points. Operation at any of these points enables the sensor to function over a large tilt range without compromising the noise performance. As well as the capacitive sensing elements, the proof mass has planar coils on the surface to electromagnetic actuator when placed in a static magnetic field. The MEMS sensor element is connected to an electronics feedback circuit similar to those used in broad-band seismometers allowing the sensor to act as a velocity output force balance transducer.